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TFC anatomy, bone architecture,

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or bone milieu for the TFC.

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TFC is, allegedly, a triangular area of fibrocartilage.

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But, once again, it doesn't look that

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triangular in the coronal projection.

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Looks like a trapezoid.

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And we've got bony structures around it,

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including the radius, the lunate, and

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the ulna distal to it, the triquetrum.

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Let's talk a little bit about the concept of variance.

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When the ulna juts forward relative to the free

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margin of the radius, we say that there is positive

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ulnar variance, and this can lead to impaction.

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But in the static scenario, in the

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asymptomatic individual who's got positive

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ulnar variance, the triangular fibrocartilage

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is going to be quite a bit thinner.

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And this is normal.

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You would expect this because there's less space.

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On the other hand, if the ulna is much shorter than the

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free distal margin of the radius, then the triangular

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fibrocartilage is going to be quite a bit thicker.

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There's also a difference in the attachments.

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When the variance is negative, in other

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words, the ulna is short relative to the

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radius, then the attachments will be longer.

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Conversely, when the distal aspect of the

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ulna is distal to the free edge of the

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radius, the attachments will be shorter.

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And by the way, when they're shorter,

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they're less prone to injury.

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Now let's talk about the relationship of

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the ulna to the radius in a static image.

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Because during the day when you

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pronate, your ulna protrudes longer.

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When you supinate, it goes back.

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When you have a firm hand grip, the tip of

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your ulna or your ulnar body goes forward.

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So it's a dynamic process.

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So measuring the variance is fraught

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with some degree of confusion.

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And you're only going to see it in one

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projection with the hand position in one place.

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So how do you assess this?

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Well, first, I look at the shape of the TFC.

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If the TFC is really thin, and they're close to

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one another, namely the ulna and the radius, I

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assume that the variance is neutral to positive.

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If the TFC is really fat, then

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odds are the variance is negative.

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Now, I do look at this relationship right here,

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and if it's greater than, say, 6 millimeters in

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one direction or the other, I will call it negative

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ulnar variance posture, or if the ulna is

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protruding forward, positive ulnar variance posture.

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And I use that posture designation because

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I know that there's some dynamic plasticity

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depending upon how the hand is positioned.

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But I use these indirect anatomic signs and

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in pathology, some of the pathologic indirect

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signs to figure out the variance scenario.

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Now, someone has come up with

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the Garcia Elias measurement.

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For assessing the overall index

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of some of these structures.

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Let's have a look at that.

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Let me change colors for a moment.

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Just to be clear.

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Let's use red.

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So let's take the tip of the styloid.

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Because this is going to be important in our

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analysis of bony milieu related to TFC anatomy and

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where the attachments go and how they're arranged.

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So we have a length of the styloid that

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we measure right here from this notch.

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We'll also have a length that is the

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difference between the distal aspect of the

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radius and the distal aspect of the ulna.

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And we'll call this B.

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We'll call the length of the styloid A.

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And then we'll measure at its

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widest point the ulnar body.

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And we'll call that C.

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So if we take A minus B over C, that should be about 0.2.

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2.

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Now, I don't make this measurement in every case.

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In fact, I hardly ever make it.

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But it just gives you a rough idea of the

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relationships of some of these structures and how

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people will calculate what's known as an Ulnar Index.

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And what is the Ulnar Index really reflecting?

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Variance and the length of the Ulnar Styloid, which

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are two very important factors in analysis of the TFC.

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Just for academic interest.

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If we had, say, B was very small, in other words,

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the ulna jutted forward and this length was less,

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then B over here would be a lower number, and that

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means that A minus B over C would be greater than 0.2.

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2.

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If this was a big number, this difference, in

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other words, we had negative ulnar variance.

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Let's look at it.

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Here's the ulna.

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Here's the radius.

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So if B was a very large number, then A

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minus B, the numerator would become a lower

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number, and we'd be substantially less than 0.2.

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109 00:05:26,215 --> 00:05:28,725 Again, not asking you to make this measurement,

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just asking you in your mind's eye to analyze the

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surrounding bony structures to get a rough idea of the

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variance, a rough idea of the discrepancy between the

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distal radius and the distal ulna, and do pay attention

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to the shape and the length of the ulnar styloid.

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Whether it's too long or too short, and

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I've given you some academic parameters

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as well as some visual parameters to use.